Recently, an imaging apparatus such as a video camera and an electronic still camera has widely spread. In each of these cameras, a solid-state imaging device such as a CCD type and an amplification type is used. In such a solid-state imaging device, a plurality of pixels having a photoelectric converter portion for generating a signal charge in accordance with an amount of incident light are formed in a grid shape.
In an amplification type solid-state imaging device, a signal charge generated and accumulated by the photoelectric converter portion in a pixel is led to an amplifying portion, and a signal amplified by the amplifying portion is output from the pixel.
In an amplification type solid-state imaging device, there is proposed, for example, a solid-state imaging device using a junction-field-effect transistor in the amplifying portion (see, for example, Japanese Patent Application Laid-Open Nos. 11-177076 and 2004-335882), and a CMOS type solid-state imaging device using an MOS transistor in the amplifying portion (see, for example, Japanese Patent Application Laid-Open No. 2004-111590).
In the conventional solid-state imaging devices disclosed in Japanese Patent Application Laid-Open Nos. 11-177076, 2004-335882 and 2004-111590, a photoelectric converter portion, an amplifying portion, and a charge-storing portion for temporally storing the charge between them are disposed in each pixel. Moreover, in the conventional solid-state imaging devices, after exposing all pixels at the same time, the signal charge generated in each photoelectric converter portion is transferred to each charge-storing portion at the same time over all pixels and temporally stored, and the signal charge is successively converted into pixel signal with a prescribed readout timing. Accordingly, it becomes possible to prevent image deformation caused by difference in exposure time of respective pixels between lines upon carrying out electronic shutter movement, which is a so-called rolling shutter.
In an imaging apparatus such as a camera, in order to realize automatic focusing control, it is necessary to detect a focal point adjusting state of an image-taking lens. Previously, a focal point detecting device was provided separately from a solid-state imaging device. However, in this case, cost increased and the apparatus became large by just the amount of the focal point detecting device and the focal point detecting optical system.
Accordingly, there has been proposed a solid-state imaging device configured to be used as a focal point detector with using a so-called pupil division phase difference detection method (sometimes called as a pupil division method or a phase difference method) as a focal point detection method (see, for example, Japanese Patent Application Laid-Open No. 2003-244712). The pupil division phase difference detection method is a method for detecting a defocusing amount of an image-taking lens such that a bundle of rays passing through the image-taking lens is divided into two at pupil to form a pair of divided images, and difference in the images, which is the amount of phase shift, is detected.
In the solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 2003-244712, a plurality of pixels having bisected photoelectric converter portions are provided. A floating diffusion is provided between one of the bisected photoelectric converter portion and the other of the bisected photoelectric converter portion, and the photoelectric converter portion is bisected by the floating diffusion. A micro-lens is provided on such photoelectric converter portions with one-to-one correspondence to each pixel. The bisected photoelectric converter portion is disposed substantially an imaging relation (conjugate relation) to the exit pupil of the image-taking lens by the micro-lens. Accordingly, since the distance between the exit pupil of the image-taking lens and the micro-lens is sufficiently larger than the dimension of the micro-lens, the bisected photoelectric converter portion is disposed substantially to the focal point of the micro-lens. In the relation described above, in each pixel, one of the bisected photoelectric converter portion selectively detects a bundle of rays passing through an area, which is a portion of the exit pupil of the image-taking lens, decentered in a given direction from the center of the exit pupil, and carries out photoelectric conversion. Moreover, in each pixel, the other of the bisected photoelectric converter portion selectively detects a bundle of rays passing through an area, which is a portion of the exit pupil of the image-taking lens, decentered in the opposite direction from the center of the exit pupil, and carries out photoelectric conversion.
In the solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 2003-244712, upon focal point detection, a signal from one of the bisected photoelectric converter portion of each pixel having the bisected photoelectric converter portion and a signal from the other of the bisected photoelectric converter portion are transferred to a floating diffusion with different timings, and red out separately. In accordance with a theory of the pupil division phase difference detection method, a state of focal point adjustment of the image-taking lens is detected on the basis of these signals. On the other hand, upon taking picture after focusing of the image-taking lens, signals from both of the bisected photoelectric converter portions are transferred to the floating diffusion at the same timing, and added in the pixel to be red out. Accordingly, since the pixel having the bisected photoelectric converter portion does not cause the same state as a defective pixel, it is excellent in view of enhancing imaging performance.
However, in the solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 2003-244712, as described above, a floating diffusion is provided between one of the bisected photoelectric converter portion and the other of the bisected photoelectric converter portion, and the photoelectric converter portion is bisected by the floating diffusion. Accordingly, since the central portion of the pixel where the incident light amount is concentrated does not have photoelectric sensitivity, when the pixel is used for taking picture upon taking picture, sensitivity of the pixel becomes low.